1. Field of the Invention
The present invention concerns a diluting and measuring device for particle counting. This device is particularly, but not exclusively, intended for the counting of blood cells.
2. Description of Related Art
It is known in the state of the art to count blood cells by causing an accurately defined volume of diluted blood sample to pass a so-called capillary, i.e., an extremely small hole, generally in a ruby, the hole having a diameter considerably larger than the size of a blood cell, typically 80 .mu.m. A voltage is applied over the capillary, and, when a blood cell passes through the hole, the electrical resistance changes. This is because the cells can be regarded as insulators. Each change in resistance can be detected by suitable electronic equipment, and the sum of all changes detected corresponds to the number of blood cells having passed through the capillary. In order to obtain the concentration of cells in the original sample, the concentration of cells in the diluted sample is multiplied by the dilution factor, typically 1:40000 when counting of red blood cells (RBC) is concerned. It is obvious, that measuring of sample volumes and dilution liquid volumes must be performed in an accurate and repeatable way such that not only a correct degree of dilution can always be guaranteed but also a thorough and uniform mixing of the two volumes is ensured.
In a typical state of the art apparatus, a syringe is employed for providing a defined volume (typically 5 ml) of diluting liquid, and this volume is displaced through a conduit to a measuring chamber. On its way to the measuring chamber, the diluting liquid brings with it a defined volume (typically 25 .mu.l) of blood sample previously introduced into the conduit. The blood sample mixes with and is diluted by the diluting liquid in the measuring chamber, which is, thus, also a dilution or mixing chamber, and a defined fraction of the diluted sample is further displaced through a capillary located in a wall of the measuring chamber, or, in a transducer located within the measuring chamber.
This state of art apparatus requires a syringe for the diluting liquid and a separate mixing/measuring chamber. It would be desirable, thus, to simplify the apparatus by combining the syringe and at least a mixing chamber.
Also, in this state of art apparatus, the mixing between the blood sample and the diluting liquid in the measuring chamber is caused by turbulence when the two liquids enter the measuring chamber and cannot be enhanced in any way. It would be desirable, thus, to enhance the turbulence in the mixing chamber, thereby to reach a more uniform mixing of the sample and the diluting liquid. One known method to achieve turbulence in a liquid is to let air bubbles into a mixing chamber at the bottom thereof by means of a pump. Evidently, the need of a pump makes the apparatus more expensive and cumbersome and increases the need of maintenance.